The University of Washington autism program project has five objectives: (1) to deepen our understanding of the neurobiological bases of autism by investigating the relation among brain structure, chemistry, and function over time; (2) to determine whether the syndrome of autism is comprised of meaningful and valid subtypes characterized by distinct etiologies, structural and metabolic brain abnormalities, neurocognitive profiles, developmental courses, and patterns of symptom expression; (3) to improve methods of early identification; (4) to identify early behavioral, neurocognitive, and biological predictors of outcome in autism, including early precursors of language and social development; and (5) to investigate the genetic basis of autism by determining the chromosomal location of autism susceptibility genes, to enhance this effort by developing quantitative autism phenotypic measures, and by using information regarding genetic heterogeneity/subtypes. There are two major parts of this program project: (1) the first part consists of a longitudinal, multi-disciplinary study of 75 children with autism spectrum disorder (ASD), 40 with developmental delay (DD), and comparison groups of CA- and MA-matched typically developing children who are being followed from infancy to age nine. Projects I - IV comprise the longitudinal study, and (2) the second part is a sibling linkage study of over 150 multiplex autism families (Project V). Information gained in the longitudinal study (Projects 1 - IV) is being used to model genetic heterogeneity and refine phenotypic measures used in the genetic linkage study (Project V). Thus, findings from all five research projects are being integrated in a synergistic way to offer a deeper understanding of the neurobiological and genetic basis of autism.